The study, titled CEOs With the Greatest Impact on Growth, puts Cook in the top spot with an astonishing $1.57 billion in average revenue growth per month during his 77 months as CEO of Apple. The study is dated April 26 but was publicized this week.

"While much of his success stems from constant innovation, breakthrough technology, and attention to branding and customer needs, we also know that that Cook's No. 1 spot can be attributed to the ubiquity of Apple products and services, as well as owning the lion's share of the market when he stepped in," the report said.

In second place is Larry J. Merlo of CVS Health, with just under $860 million in average monthly growth. Verizon's Lowell McAdam is third, followed by Alphabet/Google's Sundar Pichai, Amazon's Jeff Bezos and Disney's Robert Iger. Berkshire Hathaway's Warren Buffett, who recently increased his Apple stake, is 10th, while Facebook's Mark Zuckerberg is 18th.

"Tim Cook, CEO of Apple Inc., is perched high above the other 49 top CEOs, with an average monthly growth of nearly $1.6 billion throughout the 77 months Cook has been at the head of the table," writes the study authors. "While much of his success stems from constant innovation, breakthrough technology, and attention to branding and customer needs, we also know that that Cook's No. 1 spot can be attributed to the ubiquity of Apple products and services, as well as owning the lion's share of the market when he stepped in."

"Average monthly growth during tenure" may not be the most traditional of measures for corporate executives, especially one coming from an executive search firm that specializes in nonprofits. But it does show once again that Tim Cook's time at the helm at Apple has been a nearly unqualified success.